Background: Beliefs about one's own abilities and perspective-taking are essential for appropriate behavior in professional and social life, cooperative learning, and situations were conflict is occurring. The social comparison theory and previous research suggested positive relations between school students' beliefs about one's own abilities and perspective-taking. The hypotheses were: (1) Beliefs about one's own abilities and perspective-taking are positively related to each other after the transition to secondary school and (2) will fade thereafter. Methods: The hypotheses were tested using data from two national longitudinal studies. In Study 1, analyses were based on a sample consisting of the same N = 4428 students in fifth, seventh, and ninth grades. Beliefs about one's own abilities and perspective-taking were analyzed by one structural equation model considering relevant covariates, namely gender, school achievement, ethnic background, school type, and socioeconomic status. In Study 2, the sample consisted of N = 2105 students who were assessed at the beginning, during, and at the end of fifth grade. Beliefs about one's own abilities and perspective-taking were analyzed by the same structural equation model as in Study 1 including the same covariates and additional cognitive abilities. Results: Relations only existed from the first to the second measurement point in both studies. Conclusions: A possible explanation for the changed relationship over time is that the students adjusted to their peers, and likely learned to deal with diverse conflicting situations and to differentiate between academic, social or other abilities over the course of the school year. Perspective-taking items measure coordination between oneself and other people in social interactions and conflicting situations. In the future, such relations could be analyzed using domain-specific perspective-taking items.